The present invention relates to a semiconductor device and a manufacturing method thereof, which can be used appropriately as, e.g., a semiconductor device having a nonvolatile memory and a manufacturing method thereof.
As an electrically writable/erasable nonvolatile semiconductor storage device, an EEPROM (Electrically Erasable and Programmable Read Only Memory) has been used widely. Such a storage device represented by a flash memory which is currently used widely has a conductive floating gate electrode or trapping insulating film surrounded by oxide films under the gate electrode of a MISFET. A charge storage state in the floating gate electrode or trapping insulating film is used as stored information and read as the threshold of the transistor. The trapping insulating film refers to an insulating film capable of storing charges therein, and examples thereof include a silicon nitride film. By injection/release of charges into/from such a charge storage region, the threshold of the MISFET is shifted to allow the MISFET to operate as a storage element. Examples of the flash memory include a split-gate cell using a MONOS (Metal Oxide Nitride Oxide Semiconductor) film. In such a memory, a silicon nitride film is used as a charge storage region. This provides advantages over the case where the conductive floating gate film is used as the charge storage regions such that, due to discrete storage of charges, data retention reliability is high, and the high data retention reliability allows the oxide films over and under the silicon nitride film to be thinned and allows a voltage for a write/erase operation to be reduced.
Each of Japanese Unexamined Patent Publication Nos. 2006-41227 (Patent Document 1), 2008-288503 (Patent Document 2), and 2008-270343 (Patent Document 3) describes a technique related to a semiconductor device having a nonvolatile memory.